A vehicle may include a pressurized tank that holds fuel or some other gaseous substance that is used while the vehicle operates. For example, some vehicles operate using fuel that is supplied from a pressurized tank. The fuel is stored under pressure so that a greater quantity of fuel may be stored in the tank. Further, some high performance vehicles are supplied nitrous-oxide during high load conditions to improve engine performance. In still other vehicles, pressurized air is supplied from a tank to an engine to reduce turbocharger lag and improve vehicle launch performance. Thus, reductants, oxidants, dalliance, additives, and the like can be stored in a pressure vessel as gas, adsorbed gas, or as a liquid with a high vapor pressure.
A pressure regulator and valves are often included at the output of the storage tank to reduce the pressurized gas to a more suitable pressure for introduction to the engine. The pressurized gas may be introduced to an engine via delivery conduits including a manifold such as a fuel rail. Flow of gas from the storage tank may be stopped when pressure in the storage tank or in the delivery conduits reaches some threshold level so as not to interfere with engine operation. For example, a vehicle that operates on both gaseous and liquid fuels may switch from operating solely on a gaseous fuel to operating solely on a liquid fuel when pressure in the storage tank reaches some threshold lower pressure. If the engine were to continue operating while gaseous fuel was delivered from the storage tank, the engine might operate leaner than is desired because there might be an insufficient flow rate of fuel from the tank to the engine.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for emptying a tank, comprising: solely supplying a gaseous fuel to an engine when a pressure of the gaseous fuel is greater than a threshold pressure; and supplying the gaseous fuel and a liquid fuel when the pressure of the gaseous fuel is less than the threshold pressure.
By supplying liquid fuel and gaseous fuel to an engine when a pressure of a tank is less than a threshold, it may be possible to draw additional gas from the storage tank while providing liquid fuel to the engine so that the engine does not misfire or operate richer than is desired. For example, gas may flow from the storage tank to the engine at a lower rate than is desirable for operating the engine solely with the gaseous fuel. However, liquid fuel may be delivered along with the gaseous fuel that is arriving at a reduced rate to provide an air-fuel mixture that is desirable. Both the liquid and gaseous fuels provide energy to provide torque and rotate the engine when the mixture is combusted in a cylinder. In this way, the gaseous fuel tank may be evacuated of a pressurized gas while the engine provides acceptable performance. Further, the operating time or range of the vehicle and engine may be extended since the gaseous tank may be completely evacuated.
The present description may provide several advantages. In particular, the approach may extend engine and vehicle operating time. Further, the approach may be applicable to different types of fuel injection systems and gases. Further still, the approach may be applicable to bi-fuel and single fuel engines.
The present description provides for more completely consuming a substance stored under pressure. In one example, consuming more of a pressurized gaseous fuel may allow an operator to use more of a lower cost fuel or lower emissions fuel than would otherwise be possible in a given vehicle use cycle including refilling of both liquid and gaseous fuels. Further, in certain service situations, the approach may reduce the amount of gaseous fuel that may be vented into the atmosphere if a service procedure requires an empty gaseous fuel tank.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.